NORTH CELTIC SEA

SITE INVESTIGATION

BRIEFING DOCUMENT

1. SITE INVESTIGATION SURVEYS

A series of geophysical and geotechnical surveys will be undertaken to allow us to measure

water depth, to identify seabed features (e.g. sand waves, reefs, archaeological features),

to determine seabed sediment type and distribution (sand, mud, gravel, rock) both on and

below the seabed. We will also be carrying out ecological surveys to determine the ecology

on and in the seabed and in the water column. Oceanographic and hydrographic data on

wind speed, current speed and direction and wave height will also be recorded.

1.1. GEOPHYSICAL SURVEYS (NON-INTRUSIVE SURVEYS)

Geophysical surveys allow for the accurate prediction of

the type of material present on the seabed (e.g. rocks,

pebbles, sand/mud). Geophysical surveys involve using

acoustic devices to emit sound energy towards the

seabed. These sound waves are reflected and the

returning echoes are then detected on board the vessel.

Different echo strengths and return speeds indicate

different seabed features and different physical

characteristics. A typical survey vessel can be seen in

Figure 1.

A multibeam echosounder (MBES) is a remote sensing device

(see Figure 2) which uses sound waves to measure water depth

and sediment type. This is a non intrusive survey type and is

commonly used around the coast of Ireland. The image to the

right is a schematic of a MBES survey being carried out.

Side scan sonar (see Figure 3) is a remote sensing acoustic device produces high-

resolution mapping of the seabed in order to

investigate particular features, a wreck for example.

It is towed behind or along side the survey vessel.

A magnetometer (see Figure 4) is a passive remote sensing device that detects magnetic

fields from ferrous objects such as lost anchors, sunken ships and buried pipes on/in the

seabed. It is towed behind or along side the survey vessel. This again is a non intrusive

survey type and is in common use around

the coast of Ireland. Over the last number

of year both INFOMAR and the Marine

Institute use this type of survey on a

regular basis.

Figure 1

Figure 2

Figure 3

Figure 4

Sub bottom profiling / shallow seismic provides information on the rock and sediment

layers beneath the seabed. It is towed behind the vessel. Some examples of commonly

used sub bottom profilers can be seen in Figure 5.

The precise requirements of the geophysical survey have not yet been determined.

Depending on the size of the final survey area, it is anticipated that the geophysical survey

may take up to 3 months to complete. The anticipated timeframe for the geophysical

surveys is Q2 2021. The survey lines and timelines will be discussed in advance with local

fisheries interests and a Notice to Mariners (“NtM”) will be published in advance of the

survey.

Energia intends to have further information available on the survey specification in Q4

2020.

1.2. GEOTECHNICAL SURVEYS (INTRUSIVE SURVEYS)

In order to confirm the predictions from the geophysical surveys, representative samples

of the seabed need to be collected (ground-truthing). When the term intrusive is used, it is

indicating that a piece of equipment is used in order to

recover a sample from the seabed. Samples can be

collected by grab or core samplers. Grab samplers (see

Figure 6) collect samples to

20cm depth, gravity/box

corers (see Figure 7) collect

samples down to 40cm

depth. These samplers fall

under their own weight.

Figure 5

Figure 6

Figure 7

A vibrocore (see Figures 8 & 9) penetrates to 6m deep.

A vibrocorer uses an electrical motor that creates

vibrations that allow a metal cylinder to penetrate the

soft seabed. Cores are up to 15cm in diameter. This,

while it does penetrate the seabed, is less than 6 inches

in diameter and will backfill very quickly once the core

sample is extracted.

Piston corers (see Figure 10) can collect sediment from

15 to 30m deep, with a core diameter of c. 6.5cm. Piston

pushes core into seabed. Once the core has been retrieved

the seabed will backfill again very quickly.

Boreholes are drilled into seabed (see Figure 11). The depth of drilling depends on ground

conditions at each location and will be determined once further detail of the surveys are

available, however, they are expected to be in the region of 20-30m deep, diameter of hole

will be c.15cm.

It is envisaged that a Jack-up barge (see Figure 12) will be

used to achieve the boreholes.

Figure 9

Figure 8

Figure 11

Figure 12

Figure 10

Cone Penetration Testing (CPT) is widely

used for in-situ geotechnical characterisation

of the ground. The testing is performed with a

cylindrical penetrometer with a conical tip

(cone) pushed into the ground until it meets

resistance (see Figure 13). The example

shown right is lowered to the seabed and the

CPT operation is controlled from the surface

vessel.

Trial pits are excavated in the intertidal zone,

3m x 1m and 5m deep. They are typically dug

using an excavator (either from a boat of from

land depending on access). The pits are fully

reinstated upon completion. Trial pits will be

required in areas being examined for landfall sites (up to 10 trial pits per landfall site).

The locations of the sampling sites are unknown at this stage and will depend on the results

of the geophysical survey. The location(s) will be agreed in advance with local fisheries

interests and a NtM will be published in advance of the survey.

Energia expects to have further information available on the survey specification in Q4

2020.

Figure 13

OCEANOGRAPHIC & HYDROGRAPHIC SURVEYS

Wind speed will be recorded from a floating wind lidar buoy,

an example of which can be seen in Figures 14 & 15. It will

sit on the sea surface and be moored to the seabed. If

required for navigational safety reasons, it will be

accompanied by a marker buoy. Both buoys will be

appropriately lit and marked in accordance with the

requirements of Commissioner of Irish Lights. The location

of the Lidar buoy is not known at this stage and the buoy

may be positioned at two or more locations throughout the

monitoring campaign. The location(s) will be agreed in

advance with local fisheries interests and will be published

in a NtM. The anticipated timeframe for the installation of

the Lidar buoy is Q2 2021 for a period of 12-24 months

Current speed and direction and wave

height will be recorded by an ADCP

(Acoustic Doppler Current Profiler) which

will be bottom mounted in a trawl

resistance frame, examples of which are

shown in Figures 16 & 17. Indicative

frame dimensions are 1.5m wide by 1.5m

long and c. 0.5m high. It may be marked

at the surface by a buoy or an acoustic

release maybe used (no surface marker).

Up to 4 locations may be monitored using

an ADCP. The number of locations

monitored at any one time is unknown at

this stage as are the monitoring

location(s). The locations will be agreed in advance with local fisheries interests and will

be published in a NtM. The wave and current measurement campaign may extend for a

period of up to 24 months and it is anticipated that an initial deployment will occur in Q2

2021.

Figure 14

Figure 15

Figure 17

Figure 16

2. ECOLOGICAL SURVEYS

The marine based ecological surveys include the following:

Monthly seabird and marine mammal

surveys carried out from the M.V. Pelican

(Fastnet Shipping, Figure 18). Eighteen

transects lines (running north south) are

surveyed over a 2-day period each month

(see Figure 19). Observers on board the

vessel record sightings of seabirds and

marine mammals along each transect.

These surveys have been ongoing since

July 2019 off the coast of Co. Waterford and

will continue for a further 18 months

minimum.

Acoustic listening devices (C-PODs) will

be deployed at up to 4 locations across the

site to record marine mammal presence in

the area. A C-POD can be seen in Figure

20 and it can be deployed using an

acoustic release (also seen on the right)

with sacrificial mooring or standard bottom

mooring with surface marker buoy. These

CPODs will be attached to a clump chain

and raised approximately 3m off the

seabed. A sound-trap (to record

underwater sound) may be deployed alongside one of the CPODs for periods throughout

the monitoring campaign. The locations of the C-PODs are unknown at this stage. The

locations will be agreed in advance with local fisheries interests and will be published in a

NtM. The C-PODs will be recovered every 3 months to download the data and change

the batteries. It is anticipated that recovery will be carried out during the boat-based

monthly surveys. The initial deployment of C-PODs is anticipated for Q2 2021 and

monitoring will be required for a period of up to 24 months.

Subtidal habitat assessments will be carried out using a variety of methods depending

on sediment type, habitat type and depth. These surveys may include grab/dredge

sampling, sediment profile imagery (SPI) survey, drop-down video/ROV survey and

Figure 18

Figure 20

Figure 19

SCUBA dive survey. Sediment samples would be collected for faunal and sediment

analysis. The grab, dredge and SPI surveys would be carried out over a number of days

from a vessel similar to the M.V. Pelican. A smaller vessel would be sufficient for the

underwater video surveys and these would also be carried out over a number of days. It

is anticipated that these surveys will be carried out in Q2/Q3 2021.

Intertidal surveys would be carried out on foot between the low and high-water mark in

locations being examined as potential cable landfall sites. It is anticipated that up to 3

potential locations would be surveyed. Each location would be typically surveyed in 1 day.

Sediment samples would be collected for faunal and sediment analysis. It is anticipated

that these surveys will be carried out in Q2/Q3 2021.

FLO Contact Details

Fishery Liaisons Ltd1

Tel: 085 1147 123

Email: info@fishery-liaisons.com

1Images Sources: Chelonia – Figure 20; EdgeTech – Figure 5; Energia – Figure 19; Fastnet Shipping Ltd. – Figures 12 & 18; Fugro – Figures 11, 13 & 14; Geometrics – Figure 4; Infomar - Figures 6, 7, 9; International Ocean Systems – Figures 15 & 16; Kongsberg – Figure 5; MS Geotech - Figure 8; Pods – Figure 17; R2Sonic - Figure 2; USGS – Figures 3 & 10; XYZ Offshore - Figure 1.